1. Field of the Invention
The present invention relates to semiconductor microphone units such as silicon condenser microphones for detecting pressure variations such as sound pressure variations by use of diaphragms. The present invention also relates to manufacturing methods of semiconductor microphone units as well as methods for mounting semiconductor microphone units on substrates or circuit boards.
This application claims priority on Japanese Patent Application No. 2006-239499, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, semiconductor microphone chips such as silicon condenser microphones, which detect pressure variations such as sound pressure variations by use of diaphragms, are mounted on the surfaces of substrates or circuit boards, with which they form microphone packages. For example, Japanese Patent Application Publication No. 2004-537182 teaches a miniature silicon condenser microphone, and Japanese Patent Application Publication No. 2003-508997 teaches a pressure converter adapted to a condenser microphone system. These types of semiconductor microphone chips are each designed such that a diaphragm is arranged to cover the inner hole of a support.
The aforementioned semiconductor microphone chips are manufactured by way of manufacturing processes of semiconductor devices, in which an impurities-doped polycrystal silicon film serving as a diaphragm is formed by way of chemical vapor deposition (CVD) at a high temperature and is then cooled down so that tensile stress occurs therein.
The tensile stress reduces the deflection of the diaphragm due to pressure variations such as sound pressure variations, thus reducing the audio sensitivity.
In order to reduce the tensile stress, the diaphragm is attached to the support via a plurality of springs so that the diaphragm is distanced from the support. In this case, the diaphragm is reduced in strength when it is distanced from the support.